Note: The following are all entirely possibly artifacts of a poor software implementation:

One point looking at that is that the accelerometer they use looks like it may be sampling at a really slow rate which isn't ideal at all, maybe 30 samples per second at a guess. You can easily get into the thousands of samples per second field with a decent accelerometer, that gives a lot more detail about the moment of impact and how each shot moves through the target.

It also appears to be a pretty coarse sensor, all those shots seem to have remarkably consistent readings but looking at them, you'd think that they were fairly different.

The location of sensors is interesting as well, we were thinking about running a student project doing just this but with the sensors located on the wrist and the back of the ankles, four sensors would then probably be able to identify the types of strikes being thrown (Punches, kicks, knees and elbows) and get a sense of the quality of the technique rather than just the force it generates.

Finally, there may be an issue with maxing out the sensors read, those were pretty weak sauce strikes but the readout on them is close to maximum on that graph (although that's possibly a really trivial issue) and notice she says that the device can measure continual light strikes. That's pretty problematic.

As far as I understood the video, this device only measures the acceleration the device experiences. This is not a good indicator to measure the strenght of a punch or kick. This is because an accelerometer does not incorporate the mass (which would be a Newton(=Force)meter since force=mass*acceleration).
Because of that, it canīt differ between a punch only thrown from the shoulder and one where you put your whole weight in.
Such an instument would provide added resistance-force the farther it is pushed, which is not the case here.

Furthermore, the Force of a push is not the best indicator for the quality of a striking-technique, because it in turn does not incorporate the range the force is applied (i.e. it doesnīt include the difference of a punch being stopped on the skin and a punch which is pushed through). So you need Force*Distance which equals energy or work.

Better look for a device to measure the energy applied to a target, or at least use a newtonmeter.

Nonetheless, the device in the video is still useful for ball-sports, since the mass of e.g. a football is constant and no further force is applied after the throw.